The temperature of the world's ocean surface provides a clear indication of the regions where hurricanes and typhoons form, since they can only form when the sea surface temperature exceeds 82 degrees F (27.8 degrees C). The AMSR-E instrument on the Aqua satellite measures the temperature of the top 1 millimeter of the ocean every day, even through the clouds. In this visualization of AMSR-E data covering the period from June, 2002, to September, 2003, areas with surface temperatures greater than 82 degrees F are shown in yellow and orange, while sea surface temperatures below 82 degrees F are shown in blue. The region in the Atlantic from the Caribbean to the equator only exceeds the critical temperature during late summer and early fall in the Northern Hemisphere, the period known as Hurricane Season. It is also possible to see the Gulf Stream, the warm river of water that parallels the east coast of the United States before heading towards northern Europe, in this data. Around January 1, 2003, a cooler than normal region of the ocean appears just to the west of Peru as part of an La Nina and flows westward, driven by the trade winds. The waves that appear on the edges of this cooler area are called tropical instability waves and can also be seen in the equatorial Atlantic Ocean about the same time.
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